The present invention relates to a photo-resist composition, and more in detail, the present invention relates to an antistatic photo-resist suitable for use as a mask in ion implantation to the semiconductor substrate.
The introduction of an impurity is indispensable in the process of producing a semiconductor. Hitherto, a method of thermal dispersion has been mainly employed in the introduction of the impurity, however, in recent years, the so-called ion implantation method wherein the ions of substance to be introduced are electrostatically accelerated and implanted into a solid body has come to be mainly employed, because the control of the method is easy. Since the impurity can be doped at a low temperature by this method, it has become possible to use the photo-resist as the mask in doping. However, there has been the following demerit in using the photo-resist as the mask in doping. Namely, in the case where ions are implanted part by to the substrate, the ion implantation is carried out after forming the pattern of the .photo-resist on the part to which the ions are not to be implanted for the purpose of masking. However, the photo-resist is ordinary comprising a high polymeric substance and is non-electroconductive. Accordingly, the surface of the photo-resist is electrically charged during the ion implantation. The amount of electrical charge increases with the increase of electrical current for ion implantation, and the resulting charge becomes to cause dielectric breakdown of the insulating membrane such as silicon oxide membrane under the photo-resist. FIG. 1 of the attached drawing shows the process of causing dielectric breakdown in the ion implantation. FIG. 1(a) is the figure wherein an oxide membrane (2) is grown on a silicon substrate (1) and a photo-resist (3) is patterned further on the oxide membrane (2). FIG. 1(b) shows the manner of implantation of the ions (4).
Since the ions to be implanted are positively charged, the surface of the photo-resist is positively charged(5). FIG. 1(c) shows that the amount of electrical charge on the surface of the photo-resist increases and dielectric breakdown in the silicon oxide membrane is caused.
The electrical charge on the surface of the photo-resist at the time of ion implantation have an undesirable effect on the uniformity of the ion implantation to the substrate to be processed even though the electrical charge does not cause the dielectric breakdown of the insulating membrane under the patterned photo-resist. Namely, according to the electrical field caused by the electrical charge on the surface of the photo-resist, the ion beam is bended and accordingly, the amount of the implanted ions is the minimum at the central part of the substrate to be processed and becomes larger toward the peripheral parts of the substrate.
As is shown above, in the conventional ion implantation method, the surface of the patterned photo-resist is electrically charged, and as a result, there have been the problems such as the occurrence of dielectric breakdown in the insulating membrane under the patterned photo-resist and/or the inequality of the amount of implanted ions to the substrate to be processed.
Since the above-mentioned problems become remarkable with the increase of the amount of electric current for implanting the ions, the amount of electrical current for implanting the ions should be irresistively withhold low up to now, and the reduction of the time for the ion implantation could not be attained Besides, with the miniaturization of electric elements, the thickness of the insulating membrane such as the silicon oxide membrane, etc. becomes thinner, and accordingly, the breakdown voltage becomes lower. In such a situation, the dielectric breakdown in the insulating membrane at the time of the ion implantation has come to be an important problem furthermore.
At present, as a method of reducing the electric charge on the surface of the photo-resist pattern at the time of implanting the ions, a method wherein electrons are supplied to the vicinity of the surface of the substrate to be processed for neutralizing the electrical charge. However, in this method, it is difficult to supply the optimum amount of the electrons and there has been the problems that it is necessary to add an extra apparatus for supplying electrons to the ion implantation apparatus.
As a result of the present inventors' studies concerning the above problems, it has been found out by the present inventors that the above problems can be overcome by using the photo-resist containing an antistatic agent, and on the basis of the finding, the present invention have been accomplished.